Self-healing polymer compositions

ABSTRACT

A coating is described herein, including a material chosen from the group consisting of rubber, ceramic, metal, concrete, epoxy, polyurethane, and polyurea, a first carbon nanotube (FCN) filled with a first healing agent, wherein the first carbon nanotube has first and second ends, wherein a first FCN end cap is closed on the first end of the FCN and a second FCN end cap is closed on the second end of the FCN, and a second carbon nanotube (SCN) filled with a second healing agent, wherein the second carbon nanotube has first and second ends, wherein a first SCN end cap is closed on the first end of the SCN and a second SCN end cap is closed on the second end of the SCN, wherein the first and second carbon nanotubes are mixed in the material, wherein the end caps are removable by a hydrolysis reaction.

This application is divisional of U.S. Ser. No. 15/992,648, filed May30, 2018, now U.S. Pat. No. 10,329,436, which is a continuation-in-partof U.S. Ser. No. 15/938,016, filed Mar. 28, 2018, which is acontinuation of U.S. Ser. No. 15/070,052, filed Mar. 15, 2016, now U.S.Pat. No. 9,982,145, which is a divisional of U.S. Ser. No. 13/423,479,filed Mar. 19, 2012, now U.S. Pat. No. 9,303,171 which claims priorityto the provisional application under U.S. Ser. No. 61/451,131, entitledSELF-HEALING POLYMER COMPOSITIONS, filed Mar. 18, 2011, which isincorporated herein by reference.

BACKGROUND

This present teaching pertains to a composition that can be used to healcracks in plastics and other substrates. This present teaching alsopertains to a method of preparing a composition for healing cracks inplastics and other substrates.

DESCRIPTION OF THE RELATED ART

Cracks are detrimental to plastics, rubber, ceramics, coatings, metals,and/or concrete. Cracking may range from merely cosmetic to detrimental.The mechanisms behind cracking may vary from stress, fatigue, mechanicaldegradation, environmental factors, chemical factors, and severalothers. When a susceptible material is subjected to at least one ofthese mechanisms, cracking may occur. Because of the wide range of thesemechanisms, it may be difficult to anticipate and address the crackingbefore it is apparent.

Cracks are first nanosized, and visually unobservable. Gradually, theywill get larger. Crack formation may decrease the strength of amaterial. The cracks may then lead to deeper cracks and even corrosionissues. Crack formation may also diminish the corrosion prevention of amaterial. Besides the damaging effects of cracks, they are also visuallyundesirable. Despite quality materials, cracks will eventually beformed.

What is needed is a way to repair cracking once is has occurred withoutcompromising the integrity of the material. Ideally, what is needed is acomposition in which the material can self-heal before cracks may bevisually detected. The present teaching provides a composition that canbe used to heal cracks and a method for the preparation of thecomposition.

SUMMARY

Accordingly, it is an object of the present teaching to provide acomposition for healing cracks in a substrate comprising nanotubes; atleast one healing agent inside the nanotubes; and end caps bound ontoboth ends of the nanotubes.

One object of the present teaching is that cracks may be healed for asubstrate comprised of plastic, rubber, ceramic, coating, metal, and/orconcrete.

Another object of the present teaching is that the nanotube comprisescarbon nanotubes.

Yet another object of the present teaching is that the carbon nanotubesare single walled, double walled, and/or multiwalled.

Still another object of the present teaching is that the carbonnanotubes are functionalized.

Still yet another object of the present teaching is that the nanotubecomprises inorganic nanotubes.

One object of the present teaching is that at least one healing agent isreleased from the nanotubes for filling cracks in a substrate.

Another object of the present teaching is that a healing agent comprisesdiisocyanates, polyisocyanates, dialcohols, and/or polyalcohols.

Yet another object of the present teaching is that a healing agent isliquid.

Still another object of the present teaching is that the healing groupsof at least one healing agent are chemically protected.

Still yet another object of the present teaching is that end capscomprise polymers and/or nanoparticles.

Another object of the present teaching is that end caps comprisepolyallylamine, polylysine, aminodendrimer, aminofunctionalizedpolystyrene, and/or polyacrylate nanoparticles.

One object of the present teaching is that it provides a means forremoving the end caps and releasing the healing agent(s).

Another object of the present teaching is that it provides a means forfilling cracks in a substrate.

Another object of the present teaching is that it further comprisessilicon carbide whiskers.

Still another object of the present teaching is that it furthercomprises graphite fiber.

Still yet another object of the present teaching is that it furthercomprises nanoparticles.

Yet another object of the present teaching is that it further comprisesnanoparticles with zinc, aluminum, magnesium, and/or silver.

One object of the present teaching is a method for producing thecomposition for healing cracks comprising nanotubes, healing agent(s)inside the nanotubes, and end caps bound onto both ends of thenanotubes. The method comprises the steps of filling nanotubes withhealing agent(s) and binding end caps onto both ends of the nanotubeswherein the healing agent(s) is released from the nanotubes for fillingcracks in a substrate.

Still another object of the present teaching further comprises fillingthe healing agent(s) inside the nanotubes under vacuum.

Yet another object of the present teaching further comprises removingthe end caps and releasing the healing agent(s).

Still yet another object of the present teaching is that the end capsare removed by a hydrolysis reaction.

Another object of the present teaching is the self-healing of cracks inplastic, rubber, ceramic, coating, metal, and/or concrete.

Still another object of the present teaching is that it is easy toincorporate into a substrate.

The present teaching provides compositions and methods for efficientself-healing of cracks in plastics.

In another aspect the healing agent is encapsulated into CNTs that havebeen subsequently end-capped.

In another aspect healing agents are polyfunctional alcohols andisocyanates. Advantageously, polyalcohol is protected so that it willreact only after protecting groups have been removed, for instance, byhydrolysis.

It is a further aspect of the present teaching that healing agent(s)consist mainly of functionalized nanoparticles.

Still other benefits and advantages of the present teaching will becomeapparent to those skilled in the art to which it pertains upon a readingand understanding of the following detailed specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The present subject matter may take physical form in certain parts andarrangement of parts, embodiments of which will be described in detailin this specification and illustrated in the accompanying drawings whichform a part hereof and wherein:

FIG. 1 is a schematic representation of preparing a composition forhealing cracks in plastics and other substrates.

FIG. 2 is a schematic representation of some potential reactions of thepresent teaching.

FIG. 3 is a schematic representation of some potential reactions of thepresent teaching.

DETAILED DESCRIPTION

Referring now to the drawings wherein the showings are for purposes ofillustrating aspects of the present teaching only and not for purposesof limiting the same, and wherein like reference numerals are understoodto refer to like components, provided is a self-healing polymercomposition.

FIG. 1 shows a process for making a chemical composition for healingcracks comprising of nanotubes, at least one healing agent inside thenanotubes, and end caps, which are bound onto both ends of thenanotubes. With the chemical composition for healing cracks, the healingagent(s) can be released from the nanotubes in order to fill the cracksof various substrates. The healing agent(s) may then be released after areaction to remove the end caps has occurred.

Crack formation may be prevented, at least partially, by mixing strongnanofibers into a plastic or other substrate. The compositions presentedherein may fill these cracks and provide barrier protection againstwater and/or oxygen, which may further propagate the cracks. Thesenanofibers may provide a means to release chemical compositions whichmay self-heal various substrates when cracks begin to occur. Thesesubstrates may include plastics, rubber, coatings, ceramics, metals,and/or concrete. The substrate may be structural or used as a coating.If the substrate is a plastic, it may be thermoplastic or thermoset. Ifit is a coating, the compositions described herein may be used in moredemanding coatings applications such as oil pipes, chemical containers,and/or marine applications. With the application in coatings, thecoating formulation may contain sacrificial metal particles such as zincand/or nickel as anticorrosive agents. Nanofibers may include carbonnanotubes (CNTs) and/or inorganic nanotubes (INTs). These nanofibersprovide a vessel in which the healing agent may be held until they areneeded to fill these crack in the substrate.

The CNTs may be single walled, double walled, or multiwalled in theirlayers. Among the CNTs, the multiwalled nanotubes may have a largervolume, which may help them to hold more of the healing agents. Thesingle walled CNTs may hold less healing agent than the multiwalledCNTs. These CNTs may have excellent strength, hardness, kineticproperties, and thermal properties. CNTs can also have differentchiralities and/or can be functionalized by several methods. Forexample, the CNTs may be functionalized by amino groups and/or epoxygroups.

Inorganic nanotubes may be used an alternative or in combination withCNTs. INTs are cylindrical molecules comprised of metal oxides. TheseINTs can provide high crystallinity, good uniformity and dispersion,needle-like morphology, good adhesion to a number of polymers, and highimpact-resistance.

Additionally, silicon carbide whiskers may also be used in addition toCNTs and/or INTs. The silicon carbide whiskers may provide strength. Thesilicon carbide whiskers may also be functionalized, for example byamino groups and/or epoxy groups.

Graphite fiber may also be added for increased tensile strength. Thegraphite fiber may help to form a stronger composite or hybrid materialinto various matrix substrates.

With the nanotubes, they may be dispersed well within the substrate. Ifthe nanotubes are not dispersed well within the substrate and/or are notconnected with the polymer matrix of the substrate, the nanotubes mayglide within the substrate, which may diminish their ability to enforcethe polymer matrix, and/or the healing agent(s) may not be released whena crack(s) is formed. Thus, connecting the nanotubes with the polymermatrix of the substrate can improve its effectiveness in healing thecrack(s).

Healing agent(s) inside of the nanotubes may be used to fill the cracksand provide healing to a variety of substrates. The healing agent(s) canprovide a permanent means by which a substrate can be repaired. In thepresent teaching, one or more healing agents may be used inside thenanotubes. For example, molecular isocyanate and/or silylated alcoholmay be used. In one example, only one healing agent may be used in ananotube. Alternatively, more than one healing agent may be used in ananotube; however, there may be an interaction with another healingagent(s). In order to prevent premature reaction, at least one healingagent may be capped with protective group(s). For instance, a polyol maybe protected by trialkyl silyl groups before it is mixed withdiisocyanate. The mixture can be stable until it gets contact withwater, and silyl groups may then be hydrolyzed fast. The hydroxyl groupsmay then be exposed, and can react with isocyano groups formingpolyurethane.

Each nanotube may contain one type of healing agent or a plurality ofhealing agents within each nanotube. Further, there may be a mixture ofnanotubes in which one type of healing agent can be used inside somenanotubes and at least one other healing agent used inside othernanotubes. Healing agent(s) may include diisocyanates, polyisocyanates,dialcohols, and/or polyalcohols, which can form polyurethanes. Otherhealing agent(s) may also include diamines and/or glycolcarbonate, whichalso can form polyurethanes. Other healing agent alternatives caninclude epoxies and diamines. For example, the healing agent(s) may beaminofunctionalized where amino groups can be on the surface of CNTsthat contain diisocyanate which may react with the diisocyanate when theCNTs are filled with the healing agent(s). The healing agents may bechemically protected.

The healing agent(s) may be filled into the nanotubes under vacuum.Using this method, the nanotubes may be placed into a container that canbe evacuated. At least one healing agent may then be added such that thenanotube is covered. Once air or some other gas may be allowed into thecontainer, the nanotubes can be filled with the healing agent. Themixture with the nanotubes filled with the healing agent(s) may then befiltered and washed without removing the healing agent(s) from thenanotubes. The filtering and washing may be done using a minimal amountof inert solvent.

Healing agents may be a liquid at the temperature at which they will beused so that they may flow into crack(s) to fill them. The use of anelevated temperature may be possible if the healing agent is a solid atambient temperature or a solid in the substrate's environment. A healingagent(s) may also be dissolved in inert solvent in order to fill thenanotubes. After the filling, the nanotubes may be capped with the endcaps. If the ends of the nanotubes are not capped, the healing agent(s)may leak out prematurely.

After the healing agent(s) can be released from the nanotubes, thehealing agent(s) may solidify as a result of at least one reaction. Thisreaction may be as a result of interactions with water, oxygen, anotherhealing agent(s), and/or another material. If the healing agent(s) dosolidify after they are released from the nanotube, the volume of theresulting solid may be advantageously larger than that of the fluid formof the healing agent(s). This larger volume from the resulting solid mayaid in filling the crack(s).

Once the healing agent(s) are released, they may then work to heal thecrack(s) within the substrate. The healing agent(s) may be released in avariety of ways. First, when a crack is formed, the nanotubes may be cutat the crack site and/or the end caps, which may depend on the width ofthe end caps, such that the healing agent(s) can be released. Second,the nanotubes containing the healing agent(s) and the bound end caps mayundergo a reaction such that the end caps are removed, allowing for therelease of the healing agent(s). For the second case, this reaction maybe as a result of interactions with water. In order to trigger themechanism for releasing the healing agent, water may penetrate into thecrack(s) of the substrate. For example, if the crack is formed in ahumid environment or underwater, some water may penetrate through thecracks and into the nanotubes. Here, silyl groups may be removed byhydrolysis and excess water may be consumed. Then, some water may reactwith isocyanate compound, releasing carbon dioxide. This carbon dioxidemay act to push the healing agent(s) out of the nanotubes. The carbondioxide can also create bubbles in within the polyurethane formed fromthe healing agent(s). Also, some hydrolyzed silyl groups may polymerize,forming siloxanes.

After the nanotubes are filled with the healing agent(s), end caps maythen be bound onto the ends of the nanotubes. This capping can be donewith polymers and/or nanoparticles that may contain multiple aminoand/or hydroxyl groups. Some examples of these amino and/or hydroxylgroups may be polyallylamine, polylysine, aminodendrimer,aminofunctionalized polystyrene, and/or polyacrylate nanoparticles.These end caps may be bound with multiple bonds onto both ends of thenanotubes. They can also be on the sidewalls of the nanotubes.Additionally, the polymers and/or nanoparticles can remain free withinthe composition. If the polymers and/or nanoparticles are free, thenthey may be able to react with other chemicals within the composition.For example, amino groups may remain free and can bind with epoxy resinif the CNTs can be incorporated into the epoxy. This capping process maybe illustrated by FIG. 1.

Additionally, a second functionalization may be done within thecomposition. For example, second amino functionalized CNTs may be filledwith dialcohol and/or polyalcohols that may have amino groups on thesurface after the filling process. In another example, polyaminoparticles may be used to cap the first CNTs may be reacted withdiisocyanate, leaving one cyanate group free, and then the polyaminoparticles can bind with the amino groups at both ends and on the surfaceof the second CNTs. This reaction is also depicted in FIG. 1.

Along with the composition described herein, other microparticles and/ornanoparticles may also be added. The microparticles and/or nanoparticlesmay be filled with healing agents. The composition of the nanoparticlesmay contain metallic nanoparticles such as zinc, aluminum, magnesium,and/or silver. These metallic nanoparticles may provide a passivesacrificial galvanic protection against corrosion. These metallicnanoparticles may also offer electromagnetic interference (EMI)shielding, which may provide “immunity” for electronic components thatare susceptible to EMI and prevents the same components fromtransmitting excessive interference to their surrounding environment.

FIG. 2 depicts the use of difunctional compounds within the composition.If difunctional compounds are used, then the stoichiometry can be afactor in the length of the polymer chains. If multifunctional monomersare used, then the stoichiometry may not be as critical. For instance,if in a three-dimensional monomer one functional group does not react,or reacts with water, the remaining two functional groups can still forma polymer chain.

However, compositions with more than one healing agent may have healingagents that may leak out at different rates or be unevenly distributed.This may be a desirable property for certain types of compositions. Ifit is not desired, then it may be prevented, or at least reduced, if oneor both of the healing agents is chemically protected, and theprotecting group is cleaved by water, oxygen, and/or light. For example,if a polyurethane healing agent is used, then the alcohol may beprotected by silyl groups. With the protection from the silyl groups,viscosity may be reduced, miscibility with isocyanate components may beimproved, solid polyalcohols can have liquid silyl derivatives, and/oran excess of water can be consumed by the hydrolysis of the silylgroups. For instance, silylated glycerol and/or glucose may be used.Protecting silyl groups may be, as shown in FIG. 2, trimethyl silyl,dimethyl phenyl silyl, and/or methyl ethylenedioxy silyl. Theseprotected polyalcohols may be mixed with isocyanates and filled into thenanotubes. After capping these nanotubes, the composition may be addedto a substrate like plastic.

One aspect of the present teachings is the filling of the CNTs withhealing agent(s). When a nanocrack is formed, the CNTs may or may not becut depending on the width of the cap. If the CNTs are not wellconnected with the polymer, they might glide. In that case they will notbe useful for reinforcing the polymer in the first place. Also, thehealing agent(s) will not be released when a crack is formed. Thus,connecting the CNTs well with a polymer matrix is one aspect of thepresent teaching. Healing agent(s) should be fluids at the temperaturewhere the polymer will be used. When the healing agent(s) come out ofthe CNTs they will solidify as a result of some reaction. Reaction mayresult from interaction with water, oxygen, or it may happen between twoor several healing agents that will be released simultaneously.Advantageously, the volume of the resulting solid material is largerthan that of the fluid healing agents.

Currently favored healing agents are di-isocyanates and di- orpolyalcohols, which form polyurethanes. If the reaction happens in thepresence of water, the volume will increase many fold, because carbondioxide will be released. Polyurethane contains small bubbles, but itwill still form a good barrier against water.

In one aspect, the filling of the CNTs with healing agents happens undervacuum. The CNTs are placed into a container that is evacuated. Onehealing agent is added so that the CNT will be covered. Air or someother gas is let in, and the CNTs will be completely filled with thehealing agent. The mixture is filtered and washed with a minimal amountof inert solvent so that the contents will not be removed. In oneaspect, the healing agent is liquid during the process. Use of elevatedtemperature is possible, if the healing agent is solid at roomtemperature. The healing agent can also be dissolved into an inertsolvent. After filling, the CNTs are capped. Otherwise the healingagent(s) could leak out prematurely.

As shown in FIG. 3, the first healing agent is di-isocyanate, and thesecond healing agent is di- or polyamine. The CNTs are advantageouslyaminofunctionalized. Aminogoups that are on the surface of the firstCNTs that contain di-isocyanate will react with di-isocyanate during thefilling process. Capping is done with a polymer or nanoparticles thathave multiple amino- or hydroxyl groups, such as polyallylamine,polylysine, aminodendrimer, aminofuctionalized polystyrene, orpolyacrylate nanoparticles. Capping particles will be bound withmultiple bonds onto both ends of the CNTs, and also on the sidewalls.Many amino groups will remain free, and are able to bind with epoxyresin, if the CNTs will be incorporated into epoxy.

After the filling process, the second amino functionalized still haveamino groups on the surface. Similar polyamino particles that were usedto cap the first CNTs can be reacted with di-isocyanate so that onecyanate group remains free. The particles then bind with amino groupsthat are at both ends and on the surface of the second CNTs. The cappingprocess of the first and second CNTs is depicted in FIG. 1.

Use of difunctional compounds requires accurate stoichiometry. Otherwisepolymer chains will be very short. Use of multifunctional monomers ismuch more forgiving. For example, if in a three-functional monomer onefunctional group does not react, or reacts with water, the remaining twofunctional groups will be enough for the formation of a polymer chain.One problem with a two-component healing composition is that thecomponents may leak out at different rates or be unevenly distributed.This problem can be avoided, if one or both components are chemicallyprotected, and the protecting group is cleaved by water, oxygen, orlight. For example, if a polyurethane healing system is used, alcohol oramine may be protected by silyl groups. Silyl protecting has manyadvantages—viscosity is lowered, miscibility with isocyanate componentis improved, solid polyalcohols will have liquid silyl derivatives, andexcess water is consumed by hydrolysis of silyl groups. For example,silylated glycerol, glucose, or diaminoethane, or its oligomeric formsmay be used. Protecting silyl group may be, for example, trimethylsilyl, dimethyl phenyl silyl, or methyl ethylenedioxy silyl (FIG. 2).The protected polyalcohols may be mixed with isocyanates and the CNTsmay be filled with these mixtures. After capping the CNTs, thecomposition is mixed with plastic.

If a crack is formed in a humid environment, or under water, some waterwill penetrate inside the CNTs. Silyl groups will be removed byhydrolysis, and excess water will be consumed. Some water will reactwith the isocyanate compound, and carbon dioxide will be released.Carbon dioxide will push the mixture out of the CNT, and also createbubbles in the polyurethane. Some hydrolyzed silyl groups will be ableto polymerize on their own, forming siloxanes. The functional groups canalso be on the surface of the nanoparticles. In one aspect, thenanoparticles are small enough to fit inside of the CNTs, and themolecular isocyanate, silylated alcohol, or amine are inside the CNTs.Nanoparticles will fill most of the space inside a crack, whilemolecular components will create a final seal.

Many other kinds of nanoparticles may be used. Most notably, thecomposition may contain metallic nanoparticles, such as zinc, aluminum,magnesium, or silver. These metal particles may give passive sacrificialgalvanic protection against corrosion. They will also provide EMIshielding properties for the self-healing area.

These filled CNTs can be used to reinforce many plastics and othermaterials, including rubber, ceramics, metals, and concrete. Plasticscan be thermoset or thermoplastics. Material can be structural or usedfor coating. Epoxies, polyurethanes, and polyureas are examples. Thesecan be used in demanding coatings, such as oil pipes, chemicalcontainers, and marine applications. Coating formulations may containsacrificial metal particles, such as zinc or nickel, as anticorrosiveagents.

Also other encapsulating methods than CNTs may be used in the context ofthe present teaching.

While this present teaching has been described in detail with referenceto certain examples and illustrations of the present teaching, it shouldbe appreciated that the present teaching is not limited to the preciseexamples. Rather, in view of the present disclosure, many modificationsand variations would present themselves to those skilled in the artwithout departing from the scope and spirit of this present teaching.The examples provided are set forth to aid in an understanding of thepresent teaching but are not intended to, and should not be construedto, limit in any way the present teaching.

Example 1

Two moles ethylene glycol and one mole of tetramethyl silicate wereheated first under reflux at 60° C., and then in a distillationapparatus until no methanol was recovered. Two moles of 1,4-phenylenedi-isocyanate was added. 100 ml of the mixture was added slowly onto 50g of amino-CNTs under vacuum. The mixture was filtered using suction.Half of the amino groups in 16-aminodendrimer were reacted with butanoylanhydride. The product was dissolved into butyl propionate, and dry icecooled (about −50° C.). Filled CNTs were added slowly mixing very well.The mixture was filtered with suction and the product was mixedimmediately with the diglycidyl ether of bisphenol A.

Non-limiting aspects have been described, hereinabove. It will beapparent to those skilled in the art that the above methods andapparatuses may incorporate changes and modifications without departingfrom the general scope of the present subject matter. It is intended toinclude all such modifications and alterations in so far as they comewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A coating comprising: a material chosen from thegroup consisting of rubber, ceramic, metal, concrete, epoxy,polyurethane, and polyurea; at least a first carbon nanotube (FCN)filled with at least a first healing agent, wherein the first carbonnanotube has first and second ends, wherein a first FCN end cap isclosed on the first end of the at least one FCN and a second FCN end capis closed on the second end of the at least one FCN; and at least asecond carbon nanotube (SCN) filled with at least a second healingagent, wherein the second carbon nanotube has first and second ends,wherein a first SCN end cap is closed on the first end of the at leastone SCN and a second SCN end cap is closed on the second end of the atleast one SCN, wherein the first and second carbon nanotubes are mixedin the material, wherein the first FCN end cap, the second FCN end cap,the first SCN end cap, and the second SCN end cap are removable by ahydrolysis reaction.
 2. The coating of claim 1, wherein the at least afirst healing agent is at least two first healing agents, wherein atleast a second healing agent is at least two second healing agents,wherein at least two of a combination of the at least two first healingagents and the at least two second healing agents are different.
 3. Thecoating of claim 2, wherein one of the at least two first healing agentsis an amine and one of the at least two first healing agents is anisocyanate, wherein a functional group of the amine is chemicallyprotected by a silyl group, wherein the silyl group is capable of beingremoved by hydrolysis.
 4. The coating of claim 3, wherein the isocyanateis a diisocyanate or a polyisocyanate, and the polyamine is a diamine ora polyamine.
 5. The coating of claim 3, wherein the silyl group ischosen from the group consisting of trimethyl silyl, dimethyl phenylsilyl, and methyl ethylenedioxy silyl.
 6. The coating of claim 1,wherein the at least a first healing agent and the at least a secondhealing agent are chosen from the group consisting of molecularisocyanate, silylated alcohol, and amine.
 7. The coating of claim 1,wherein the at least a FCN and the at least a SCN are at least one layerof a single walled layer, a double walled layer, and a multiwalledlayer.
 8. The coating of claim 7, wherein the at least a FCN and the atleast a SCN are functionalized.
 9. The coating of claim 8, wherein thefirst and second FCN end caps and the first and second SCN end caps arepolymers or nanoparticles.
 10. A coating composition comprising: amaterial chosen from the group consisting of rubber, ceramic, metal,concrete, epoxy, polyurethane, and polyurea; at least a first carbonnanotube (FCN) filled with at least a first healing agent, wherein theat least a FCN has first and second ends; a first FCN end cap on thefirst end of the at least a FCN, wherein the first FCN end cap isclosed; a second FCN end cap on the second end of the at least a FCN,wherein the second FCN end cap is closed; at least a second carbonnanotube (SCN) filled with at least a second healing agent, wherein theat least a SCN has first and second ends; a first SCN end cap on thefirst end of the at least a SCN, wherein the first SCN end cap isclosed; and a second SCN end cap on the second end of the at least aSCN, wherein the second SCN end cap is closed wherein the first andsecond carbon nanotubes are mixed in the material, wherein the at leasta FCN and the at least a SCN are functionalized, wherein the first andsecond FCN end caps and the first and second SCN end caps are polymersor nanoparticles.
 11. The coating of claim 10, wherein at least a firsthealing agent is at least two first healing agents, wherein one of theat least two first healing agents is an amine and one of the at leasttwo first healing agents is an isocyanate, wherein a functional group ofthe amine is chemically protected by a silyl group, wherein the silylgroup is capable of being removed by hydrolysis.
 12. A coatingcomposition comprising: a material chosen from the group consisting ofrubber, ceramic, metal, concrete, epoxy, polyurethane, and polyurea; atleast a first carbon nanotube (FCN) filled with at least a first healingagent, wherein the at least a FCN has first and second ends; a first FCNend cap on the first end of the at least a FCN, wherein the first FCNend cap is closed; a second FCN end cap on the second end of the atleast a FCN, wherein the second FCN end cap is closed; at least a secondcarbon nanotube (SCN) filled with at least a second healing agent,wherein the at least a SCN has first and second ends; a first SCN endcap on the first end of the at least a SCN, wherein the first SCN endcap is closed; and a second SCN end cap on the second end of the atleast a SCN, wherein the second SCN end cap is closed wherein the firstand second carbon nanotubes are mixed in the material, wherein the firstand second FCN end caps and the first and second SCN end caps arepolymers or nanoparticles.
 13. The coating of claim 12, wherein thefirst FCN end cap, the second FCN end cap, the first SCN end cap, andthe second SCN end cap comprise at least one chemical of polyallylamine,polylysine, aminodendrimer, aminofunctionalized polystyrene, andpolyacrylate nanoparticles.
 14. The coating of claim 12, wherein one ofthe at least two first healing agents is an amine and one of the atleast two first healing agents is an isocyanate, wherein a functionalgroup of the amine is chemically protected by a silyl group, wherein thesilyl group is capable of being removed by hydrolysis.
 15. The coatingof claim 14, wherein the nanoparticles comprise at least one metal ofzinc, aluminum, magnesium, and silver.
 16. The coating of claim 15,wherein the at least a FCN and the at least a SCN are functionalized.17. The coating of claim 16, wherein the first FCN end cap, the secondFCN end cap, the first SCN end cap, and the second SCN end cap arecapable of being removed by hydrolysis.